It looks like you have chlorosis, as mentioned - one way to solve that very easily is to dissolve about a level teaspoon of Epsom salt (MgSO4) in a liter of water, and water with that about once a month - it both, reduces the pH of the soil, and supplies magnesium and sulfur, which a lot of houseplant fertilizers do not give enough of. Note, if you have a lot of calcium accumulation in the soil, the first time you water with MgSO4, you should make up a lot of the solution, and run several liters of it through the soil to flush it, allowing it to drain out freely.
Chlorosis is something to which citrus and chili plants are also very susceptible to, as are many other acid-loving plants. Hope this helps!
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fig leaf
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